docs: def get_index(self, label):
          """
          Find the index of the input ``label``.
  
          Parameters
          ----------
          labels : int
              The label numbers to find.
  
          Returns
          -------
          index : int
              The array index.
  
          Raises
          ------
          ValueError
              If ``label`` is invalid.
          """
  
          self.check_labels(label)
          return np.searchsorted(self.labels, label)